Hill Reaction Research Articles

Synthesis and Hill Inhibitory Activity of New Substituted 3‐Aryl‐5‐cyano‐6‐methylthio Pyrimidine‐2, 4‐diones

AbstractNovel substituted derivatives of 3‐aryl‐5‐cyano‐6‐methylthiopyrimidine‐2, 4‐diones were synthesized by the reaction of ethyl 2‐cyano‐3,3′‐dimethylthioacrylate with arylureas in good yields. The structures of all title compounds were evaluated by elemental analyses and 1H NMR spectra and compound 2c was also confirmed by X‐ray diffraction. Hill reaction inhibitory activity of title compounds was assayed.

Responses of Phaseolus Vulgaris Chromium and Cobalt Treatments

The effects of Cr and Co supplied either individually or mixed together in the nutrient solution on seed germination, enzyme activities, photosynthesis, metabolic products, and yield were investigated. Cr and Co reduced germination percentage only at the highest concentration used but markedly decreased radicle growth which might be attributed to depressive effect of Cr and Co on the activity of amylases and subsequent transport of sugars to the embryo axes. Protease activity, on the other hand, increased with the metal treatment. The highest concentration (10-2 M) tested of both metals was harmful on plant growth, while the low and moderate concentrations (10-6 and 10-4 M) enhanced the contents of chlorophylls and sugars, and activity of Hill reaction. Fresh mass of the produced pods increased at low and moderate concentrations of Cr and at Cr+Co treatment, but decreased in plants treated with Co.

Annonaceous acetogenins: Naturally occurring inhibitors of ATP synthesis and photosystem II in spinach chloroplasts

The effects of squamocin (1), bullatacin (2) and motrilin (3), 3 bis‐tetrahydrofuran Annonaceous acetogenins, isolated from Annona purpurea (Annonaceae), were investigated on several photosynthetic activities in spinach thylakoids. The results indicated that compounds 1–3 significantly inhibited both ATP synthesis and uncoupled electron transport. In addition, they enhanced light‐activated Mg2+‐ATPase, and basal electron flow. Therefore, acetogenins 1–3 behave as uncouplers and Hill reaction inhibitors. Natural products 1–3 did not affect photosystem I (PSI) activity but they inhibited photosystem II (PSII) electron flow. The study of the partial PSII reactions from H2O to DCPIPox, H2O to SiMo and diphenylcarbazide to DCPIP established that the site of inhibition was at the oxygen‐evolving complex (OEC). Chlorophyll a fluorescence measurements confirmed the behavior of the Annonaceous acetogenins as water‐splitting enzyme inhibitors.

Inhibition of Photophosphorylation and Electron Transport by Flavonoids and Biflavonoids from Endemic Tephrosia spp. of Mexico

Abstract The biflavonoids tepicanol 1 and crassifolin 2 and the flavonoids elongatin 3, tephrobotin 4, tephroleocarpin 5, glabranin 6, and methylglabranin 7 were isolated from Tephrosia tepicana, T. crassifolia, T. viridiflora, T. abbottiae, T. leiocarpa, and T. madrensis, respectively, Leguminoseae-Papilionidae, a large tropical and subtropical genus, and their in vitro effects on different photosynthetic activities were investigated. All the compounds isolated, except 1 and 3, induced a concentration-dependent inhibition of photophosphorylation. Compounds 2 and 4-7 interfered with the energetic metabolism of plants at the level of photosynthesis with different mechanisms of action. Compounds 2, 4, and 6 behave as Hill reaction inhibitors, and compounds 5 and 7 act as energy transfer inhibitors (H+-ATPase inhibitor).

The Effect of Heat Shock on the Capacity of Wheat Plants to Restore Their Photosynthetic Electron Transport after Photoinhibition or Repeated Heating

The shoots of 16-day-old spring wheat plants (Triticum aestivumL., cv. Albidum 29) were subjected to heat shock (HS) at 40, 41, or 43°C for 10 min. The activity of the Hill reaction in chloroplasts isolated immediately after HS was 83, 61, and 30% of the initial value, respectively. The activity of the Hill reaction was also estimated after plant return to the initial growth conditions for one day. It was completely restored after heating at 40°C and achieved 82 and 30–33% of the initial level after heating at 41 and 43°C, respectively. Thereafter, the shoots were heated repeatedly at 42, 43, or 43.5°C for 10 min, and the activity of the Hill reaction was measured immediately or one day after this heating. Immediately after the second heating, the activity decreased again as compared to its value before heating. The percent of inhibition of the Hill reaction was similar in the control plants not subjected to preliminary HS and HS-treated plants independently of the temperature used. However, after one-day growth under normal conditions, the activity of the Hill reaction was restored almost completely in HS-treated plants but not more than by 10% in the control plants. The conclusion is that different mechanisms underlie the development of the tolerance to HS and recovery. Some plants were tested for the effect of HS (40°C) on their tolerance to photoinhibition. The degree of the Hill reaction inhibition after plant exposure to the light of 65–75 klx for 3 h was essentially similar in detached leaves from the HS-treated and unheated plants and comprised about 40% of the activity before light stress. After the leaves were returned to the low-light conditions for 3 h, the Hill reaction was restored and attained about 75% of that before photoinhibition in both HS-treated and untreated plants. The lack of the HS-induced stimulation of the Hill reaction recovery after photoinhibition is evidently related to the fact that heating and excess light damage different sites of photosystem II, which implies the different pathways for the recovery of its functional activity.

Hydrogen peroxide inhibits photosynthetic electron transport in cells of cyanobacteria.

The effect of H2O2 on photosynthetic O2 evolution and photosynthetic electron transfer in cells of cyanobacteria Anabaena variabilis and Anacystis nidulans was studied. The following experiments were performed: 1) directly testing the effect of exogenous H2O2; 2) testing the effect of intracellular H2O2 generated with the use of methyl viologen (MV); 3) testing the effect of inhibiting intracellular H2O2 decomposition by salicylic acid (SA) and 3-amino-1,2,4-triazole (AT). H2O2 inhibited photosynthetic O2 evolution and light-induced reduction of p-benzoquinone (BQ) + ferricyanide (FeCy) in the Hill reaction. The I50 value for H2O2 was ~0.75 mM. Photosynthetic electron transfer in the cells treated with H2O2 was not maintained by H2O2, NH2OH, 1,5-diphenylcarbazide, tetraphenylboron, or butylated hydroxytoluene added as artificial electron donors for Photosystem (PS) II. The H2O --> CO2, H2O --> MV (involving PSII and PSI) and H2O --> BQ + FeCy (chiefly dependent on PSII) electron transfer reactions were inhibited upon incubation of the cells with MV, SA, or AT. The N,N,N,N-tetramethyl-p-phenylenediamine --> MV (chiefly dependent on PSI) electron transfer was inhibited by SA and AT but was resistant to MV. The results show that H2O2 inhibits photosynthetic electron transfer. It is unlikely that H2O2 could be a physiological electron donor in oxygenic photosynthesis.

Lighting the path:a tribute to Robert Emerson (1903-1959)

Today, we shall re-live the discoveries of the basic concepts of the light reactions of oxygenic photosynthesis. The concept of the Photosynthetic Unit, and the quantum efficiency emerged as early topics of quantitative studies. Determination of the minimum number of quanta needed for the release of one O2 molecule had a long and bitter controversy. According to Otto Warburg (1883-1970), the minimum quantum requirement per O2 was between 2.8 and 4. The experiments of Robert Emerson (1901-1959), on the other hand, gave values of 8 to 12. The latter range was finally accepted. A number of important basic discoveries led to support the two-light reaction/two photosystem scheme of photosynthesis that we now use as the basis of design of further research. These discoveries will be considered, and include: the Emerson Enhancement Effect, the Hill Reaction, and the existence of different spectral forms of Chl a. Several kinds of experimental evidence reinforced the two-light/two-photosystem concept; the researches of Bessel Kok, Lou Duysens, Jan Amesz and Horst Witt were particularly significant. The theoretical ideas of Hans Gaffron, James Franck and Eugene Rabinowitch, the experiments of William Arnold, Larry Blinks, and C. Stacy French, and the challenges of Daniel Arnon added much spice to the evolution of our current understanding. It was, however, the biochemical insights of Robin Hill (1899-1991) that rationalized the diverse kinds of evidence that accounted for the experimental facts in terms of the two-light/two-photosystem mechanism, popularly known as the Z? scheme.

Effect of lanthanide chloride on photosynthesis and dry matter accumulation in tobacco seedlings.

To investigate the physiological effects of rare earth ions, we have studied the effect of LaCl3 on the photosynthetic light reactions in tobacco (Nicotiana tobacum). When treated with 5-20 mg/L LaCl3 in Hoagland solution by water culture, the dry matter accumulation of different parts in tobacco, the content of chlorophyll increased gradually, but decreased when the concentration of LaCl3 was > or = 50 mg/L. The optimum concentration for growth appeared to be about 20 mg/L of LaCl3 in nutrient solution. La3+ promoted the activities of the Hill reaction, Mg2(+)-ATPase, and stimulated the rate of photophosphorylation in chloroplast at low concentrations, but inhibited them at high concentrations. It is concluded that La3+ stimulated the growth of tobacco seedlings and accelerated the photosynthetic light reactions at suitable concentration in vivo.

Photosynthesis in Two Wheat Cultivars Differing in Salt Susceptibility

Salinised (150 mM NaCl for 15 d) roots excised from salt sensitive wheat cultivar Giza 163 showed about 15-fold increase in the ratio of Na/K while salt tolerant Sakha 92 exhibited only 7.5-fold increase compared to their control ratios. Root ratio of saturated/unsaturated fatty acids was stimulated twice in the sensitive cultivar versus 1.7-fold increase in the tolerant ones. Salinity enhanced greatly the accumulation of spermine (Spm) and spermidine (Spd) contents associated with a decrease in putrescine (Put) content in both wheat cultivars. Higher ratios of Spm+Spd/Put associated with lower content of proline and low ethylene evolution were detected in shoots and roots of salt tolerant cultivar. Chlorophyll a/b ratio showed an increase from 1.3 in control of both cultivars to 1.6 and 1.4 in stressed Giza 163 and Sakha 92, respectively. A reduced Hill reaction activity (19 %) was observed in stressed chloroplasts isolated from leaves of the tolerant cultivar versus 40 % inhibition in the sensitive ones. Moreover, chloroplasts isolated from stressed leaves of the sensitive cultivar showed about 25 % reduction in fluorescence emission at 685 nm as well as shifts in the peaks in the visible region.

Deficiency of manganese is alleviated more by low zinc than low copper in wheat

Wheat (Triticum aestivum L.) var. Sonalika was grown in purified sand in complete nutrient solution (normal), deficient manganese (Mn) (0.0055 mg L‐1), deficient copper (Cu) (0.0065 mg L‐1), deficient zinc (Zn) (0.0065 mg L‐1), deficient ?n/deficient Cu, deficient ?n/deficient Zn, deficient Cu/deficient Zn, and deficient ?n/deficient Cu/deficient Zn treatments. The deficiency of Mn decreased the biomass, concentration of Mn, chlorophyll, sugars, Hill reaction activity, acid phosphatase activity, and increased that of peroxidase and polyphenol oxidase. The magnitude of Mn deficiency effects was mitigated to variable extent when Mn was deficient along with deficient Cu and/or deficient Zn. The effects of either Cu or Zn deficiency viz., intensification of foliar symptoms, decrease in biomass, leaf Cu/Zn, seed yield and starch content were increased further in combined deficiency of Cu and Zn. The stimulation in acid phosphatase and decrease in the activity of polyphenol oxidase and carbonic anhydrase in Cu or Zn deficient leaves were further aggravated when both Cu and Zn were deficient together. All these changes reveal a synergism between Cu and Zn in wheat.

Photosynlhetic Inhibitory Activity of Dihydro-β-agarofurans Sesquiterpenes from Maytenus dislicha and Maytenus boaria (Celastraceae)

Abstract The effects of 9β-benzoyloxy-la, 2α, 6β, 8α, 15-pentaacetoxy-dihydro-β-agarofuran and 9β furoyloxy-1α, 6β, 8α-triacetoxy-dihydro-β-agarofuran, major phytogrowth inhibitors isolated from the aerial parts of Maytenus disticha (Celastraceae) and seeds of Maytenus boaria (Celastaraceae), respectively, on different photosynthetic activities of isolated spinach chloroplasts have been investigated. Photophosphorylation and electron transport (basal, phosphorylating and uncoupled) were inhibited in a concentration dependent manner by both compounds, therefore acting as Hill reaction inhibitors. The site of action of these natural compounds was located in the span from P680 to QA. 9β-benzoyloxy-1,2,6,8,15-pentaacetoxydihydro-β-agarofuran was one order of magnitude more potent (I50 = 2.6 μм) than 9β-furoyloxy-1,6,8,-triacetoxydihydro-β-agarofuran, suggesting that the substitution at C-9 and the acetoxy groups at carbons 2 and 15 are important structural requirements for the displayed inhibitory activity.

Identification of Two Mechanisms of Atrazine Resistance in Setaria faberi and Setaria viridis Biotypes

Abstract Two resistant (R) biotypes of Setaria faberi and S. viridis have been detected in maize fields continuously treated with triazine herbicides. The R biotypes of S. faberi and S. viridis were 10.0 and 6.5 times, respectively, more resistant to atrazine than their susceptible (S) biotypes. Both R biotype plastids had less affinity for atrazine than the S biotypes based on chlorophyll fluorescence and Hill reaction assays. As expected, they exhibited cross-resistance to a wide variety of photosystem II inhibitors. The hierarchy of resistance level of these two biotypes was chloro- s -triazines ⪢ methoxy- s -triazines > methyltio- s -triazines ≥ as-triazines. There was no difference in the absorption and translocation of [ 14 C]atrazine in R and S biotypes. Fast fluorescence induction curves showed that atrazine inhibited whole-leaf photosynthesis in S biotypes and they later recovered slight fluorescence activity in both populations. All biotypes produced the same pattern of metabolites, but the R biotypes detoxified the atrazine to conjugate-atrazine at a higher rate than the S biotypes (R > 75% > S). The five wild-type Setaria spp. found in Spain showed differences in detoxification of atrazine. The hierarchy of detoxifying level of atrazine of these Setaria spp. was S. verticilata ≃ S. adherens ⪢ S. faberi ≃ S. viridis >⪢ S. glauca .

Effect of Indol-3-yl Acetic Acid on Photosynthetic Characteristics of Wheat Flag Leaf During Grain Filling

Area and fresh and dry masses of flag leaf show two phases of development during grain filling in Triticum aestivum. The initial large increase in leaf size is mainly due to water intake. Contents of chlorophylls and carotenoids, reducing sugars, and sucrose, Hill reaction rate, and photosynthetic activity increased during leaf growth, but a noticeable decline in these parameters followed throughout leaf senescence. The maximum accumulation of polysaccharides and proteins occurred at the beginning of grain set, but a continuous decline in their absolute values was manifested during grain filling. Grain priming with indol-3-yl acetic acid (IAA) at 25 mg kg-1 stimulated the flag leaf growth, namely its fresh and dry masses and its area. Furthermore, the stimulatory effect was mainly due to the increase in the pigment formation that in turn increased the photosynthetic activity of flag leaf during grain filling. On the other hand, the highest dose of IAA (50 mg kg-1) attenuated the growth and physiological activity of flag leaf through its inhibitory action on leaf fresh and dry masses, leaf area, pigments, saccharides and protein formation, as well as its effect on 14CO2 assimilation.

The immobilization of microbial cells, subcellular organelles, and enzymes in calcium alginate gels. Reprinted from Biotechnology and Bioengineering, Vol. XIX, No. 3, Pages 387-397 (1977).

Saccharomyces cerevisiae cells, Kluyveromyces marxianus cells, inulase, glucose oxidase, chloroplasts, and mitochondria were immobilized in calcium alginate gels. Ethanol production from glucose solutions by an immobilized preparation of S. cerevisiae was demonstrated over a total of twenty-three days, and the half-life of such a preparation was shown to be about ten days. Immobilized K. marxianus, inulase, and glucose oxidase preparations were used to demonstrate the porosity and retraining properties of calcium alginate gels. Calcium alginate-immobilized chloroplasts were shown to perform the Hill reaction. Some experiments with immobilized mitochondria are reported.

Effect of white and red light on the pigment content and functional activity in pine chloroplasts.

The pigment content and rates of primary photosynthetic reactions were determined in chloroplasts of 14-day-old pine (Pinus silvestris L.) seedlings grown in light and darkness. In addition, the functional activities were investigated in chloroplasts from dark-grown seedlings exposed to white, red (λ = 670 nm), and red + far-red (λ = 748 nm) light. Dark-grown seedlings were capable of performing the Hill reaction, noncyclic photophosphorylation, and phenazine methosulfate–supported photophosphorylation, although the reaction rates in chloroplasts from dark-grown plants were considerably lower than in preparations from light-grown plants. Light treatment of dark-grown seedlings rapidly activated the photoreduction of ferricyanide and photophosphorylation, while the additional accumulation of green pigments started only after a lag period of two hours. Preirradiation of dark-grown seedlings with red light stimulated the formation of pigments, especially chlorophyll b, as well as the functional activity of chloroplasts. When far-red light was applied after red-light exposure, the processes examined were inhibited. It is concluded that accumulation of the light-harvesting complex and functional activities of chloroplasts at the photosystem II level in pine seedlings are controlled by the phytochrome.

The Development of Chloroplast Ultrastructure and Hill Reaction Activity During Leaf Ontogeny in Different Maize (Zea Mays L.) Genotypes

Changes in Hill reaction activity (HRA) and ultrastructure of mesophyll cell (MC) chloroplasts were studied during the ontogeny of third leaf of maize plants using polarographic oxygen evolution measurement, transmission electron microscopy, and stereology. The chloroplast ultrastructure was compared in young (actively growing), mature, and senescing leaves of two different inbreds and their reciprocal F1 hybrids. Statistically significant differences in both HRA and MC chloroplast ultrastructure were observed between different stages of leaf ontogeny. Growth of plastoglobuli was the most striking characteristic of chloroplast maturation and senescence. The chloroplasts in mature and senescing leaves had a more developed system of thylakoids compared to the young leaves. Higher HRA was usually connected with higher thylakoid volume density of MC chloroplasts.

Uniconazole (S-3307) Induced Protection of Abelmoschus Esculentus L. Against Cadmium Stress

In Abelmoschus esculentus L. uniconazole brought about a marked decrease in cadmium-induced loss of chlorophyll and Hill reaction activity, but it did not completely prevent cadmium toxicity.

Structural and Functional Damage Caused by Boron Deficiency in Sunflower Leaves

Boron deficiency induced a dramatic inhibition in sunflower plant growth, shown by a reduction in dry mass of roots and shoots of plants grown for 10 d in nutrient solution supplied with 0.02 µM B. This low B supply facilitated the appearance of brown purple pigmentation on the plant leaves over the entire growth period. Compared to B-sufficient (BS) leaves, leakage from B-deficient (BD) leaves was 20 fold higher for potassium, 38 fold for sucrose, and 6 fold for phenolic compounds. High level of membrane peroxidation was detected by measuring peroxidase activities as well as peroxidative products in BD sunflower plants. Soluble and bound peroxidase activities measured in BD thylakoid membranes were accelerated two fold compared to those detected in BS-membranes. No detectable change in soluble peroxidase activity in roots whereas a 4 fold stimulation in bound peroxidase activity was detected. Thylakoid membranes subjected to low B supply showed enhancement in lipoxygenase activity and malondialdehyde (MDA) content in parallel with 40 and 30 % decrease of linoleic and linolenic acid contents (related to total unsaturated fatty acids). A slower rate of Hill reaction activity (40 %) and a suppressed flow of electron transfer of the whole chain (30 %) were detected in BD thylakoid membranes. This reduction was accompanied with a decline in the activity of photosystem 2 shown by a diminished rate of oxygen evolution (42 %) coupled with a quenching (27.5 %) in chlorophyll a fluorescence emission spectra at 685 nm (F685). Thus B is an important element for membrane maintenance, protection, and function by minimizing or limiting production of free oxygen radicals in thylakoid membranes of sunflower leaves.

Photoadaptation in the Green Alga Spongiochloris Sp. A Three-Fluorometer Study

The dark-adapted cells of the green alga Spongiochloris sp. were exposed to "white light" of 1000 µmol(photon) m-2 s-1 for 2 h and then dark adapted for 1.5 h. Changes of photochemical activities during photoadaptation were followed by measurement of chlorophyll (Chl) fluorescence kinetics, 77 K emission spectra, photosynthetic oxygen evolution, and pigment composition. We observed a build-up of slowly-relaxing non-photochemical quenching which led to a decrease of the Fv/Fm parameter and the connectivity. In contrast to the depression of Fv/Fm (35 %) and the rise of non-photochemical quenching (∼ 1.6), we observed an increase in effective absorption cross-section (20 %), Hill reaction (30 %), photosynthetic oxygen evolution (80 %), and electron transport rate estimated from the Chl fluorescence analysis (80 %). We showed an inconsistency in the presently used interpretation schemes, and ascribe the discrepancy between the increase of effective absorption cross-section and the photosynthetic activities on one side and the effective non-photochemical quenching on the other side to the build-up of a quenching mechanism which dissipates energy in closed reaction centres. Such a type of quenching changes the ratio between thermal dissipation and fluorescence without any effect on photochemical yield. In this case the Fv/Fm ratio cannot be used as a measure of the maximum photochemical yield of PS2.

Two Inhibition Targets by [Cr(2gb)3]3+ and [Co(2gb)3]3+ on Redox Enzymes of Spinach Thylakoids

[Cr(2gb)(3)]Cl(ZnCl(4)), [Cr(2gb)(3)]Cl(3), and [Co(2gb)(3)]Cl(3) were synthesized and characterized. Their chemical structures and the oxidation states of their metal centers remained unchanged in solution. The effects of these compounds, CrCl(3) and [Co(NH(3))(6)]Cl(3), on photosynthesis were investigated. The coordination compounds inhibit ATP synthesis and electron flow (basal, phosphorylating, and uncoupled), behaving as Hill reaction inhibitors. The target for [Cr(2gb)(3)]Cl(ZnCl(4)) is located at the Q(B) level. In contrast, the interaction sites of [Cr(2gb)(3)]Cl(3) and [Co(2gb)(3)]Cl(3) are located in the span from P(680) to Q(A) and at the b(6)f complex. Neither CrCl(3) nor [Co(NH(3))(6)]Cl(3) inhibited photosynthesis. The 100% inhibition on PS II of [Cr(2gb)(3)]Cl(ZnCl(4)) is explained in terms of a synergystic effect between the 2gb-chromium(III) coordination compound and the ZnCl(4)(2)(-) anion.